Circle Calculator - Free Online Circle Area & Circumference Calculator
Circle Calculator
Calculate any circle property by entering one known value. The calculator will find area, circumference, diameter, and radius.
How to use this calculator
📐 How to Use the Circle Calculator
- Select what circle property you know (radius, diameter, circumference, or area)
- Enter the known value in the input field
- Choose your preferred unit of measurement
- Click "Calculate Circle Properties" to get all circle measurements
- View the visual diagram and all calculated properties
📏 Circle Formulas
Circumference (C):
C = 2πr = πd
The distance around the circle
Area (A):
A = πr² = π(d/2)²
The space enclosed by the circle
Diameter (d):
d = 2r
The distance across the circle through its center
🌟 Real-World Examples
Example 1: Pizza Size
A 12-inch pizza has a diameter of 12 inches. Its radius is 6 inches, circumference is 37.7 inches, and area is 113.1 square inches.
Example 2: Running Track
A circular track with a radius of 50 meters has a circumference of 314.16 meters. One lap around the track is approximately 314 meters.
Example 3: Garden Design
To create a circular garden bed with an area of 20 square meters, you need a radius of 2.52 meters or a diameter of 5.05 meters.
💡 Pro Tips
- • Remember that π (pi) ≈ 3.14159 for quick mental calculations
- • When measuring circles in real life, diameter is often easier to measure than radius
- • For area calculations, remember that doubling the radius quadruples the area
- • The circumference-to-diameter ratio is always π, regardless of circle size
- • Use consistent units - area will be in square units (m², ft², etc.)
⚠️ Common Mistakes to Avoid
- • Don't confuse radius with diameter - radius is half the diameter
- • Remember to square the radius for area calculations, not just multiply by 2
- • Always use the same units throughout your calculation
- • Don't forget that area results are in square units
- • Ensure you're using the correct value of π for your required precision
About this calculator
Calculate circle area, circumference, diameter, and radius instantly. Free online circle calculator with visual diagram and step-by-step solutions.
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